Television field-identification system



D. RICHMAN TELEVISION FIELD-IDENTIFICATION SYSTEM Original Filed Nov.30, 1951l July 28, 1959 4 Sheets-Sheet l Jly 28, 1959 D. RICHMAN2,897,266

TELEVISION FIELD-IDENTIFICATION SYSTEM Original Filed Nov. 30, 1951 4Sheets-Sheet 2 I I I l I I I I I l l I I I I I "f- Tlc P DETECTOR +B63,.a TRICGER |37 CIRCUIT 97 CIRCUIT g L :0J l 0|OI l Tso e2 B6 80 95 y96 l as i I If 94 Il 1 l FIGS I I 37 O+S I I I I I I I I I I I INVENToR.FIG.6 DONALD RICHMAN ATTORNEY July 28, 1959 D. Rlcl-IMAN TELEVISIONFIELD-IDENTIFICATION SYSTEM Original Filed Nov. 3.0, 1951 4 Sheets-Sheet3 FIG. 30

INVENTOR. DONALD RICH MAN ATTORNEY July 28, 1959 D. Rlcl-IMAN TELEVISIONFIELD-IDENTIFICATION SYSTEM Original Filed Nov. 30, 1951 4 Sheets-Sheet4 BO+BMO+BO+4 INVENTUR DONALD RICH MAN FIG. 4

ATTORNEY United States Patent O TEDEVISION FIEIJD -IDENTIFICATION SYSTEMDonald Richman, Fresh Meadows, `N.Y., assignor t Hazeltme Research,'Inc., Chicago, Ill., a corporation of Illinois Continuation ofapplication Serial No. 259,171, November 30, 1951. This applicationNovember 16, 1956, Serial No. 623,279

General This invention relates to iield-identication systems forconventional television systems of the` odd-line interlaced type and,particularly, for color-television systems utilizing such interlacingtor determining vwhether a field being scanned is composed of odd oreven lines of scan.k The present invention is directed to an improvementin the field-identification system described in applicants copendingapplication, Serial No. 244,756, filed September 1, 1951 (now UnitedStates Patent No. 2,697,- 744), and entitled TelevisionField-Identification System.

This application is a continuation-in-whole of application Serial No.259,171, filed November 30, 1951, now abandoned.

In a for-m of color-television system more completely described in theRCA Review for December 1949, volume X, at pages S04-524, inclusive,color signals individually representative of the basic colors,specifically green, red, and blue of a color image being televised, aredeveloped at a transmitter and components of these signals are appliedas modulation signals to a subcarrier wave signal eiectively to modulatethe latter signal in a predetermined phase sequence. Conventionally, themodulated subcarrier ywave signal has a predetermined frequency lessthan the highest video frequency and has amplitude and phasecharacteristics related to the basic colors of the televised image. In aspeciiic form of such system the subcarrier wave signal is effectivelymodulated at 120 phase points by successive ones of the three basiccolorsignal components. At any one time the green, red, and bluecolor-signal components may modulate the subcarrier in the order inwhich they are mentioned. At another time, as described in copendingapplication, Serial No.

207,154, VBernard D. Loughlin, entitled Color-Television System, and ledJanuary 22, 1951, now abandoned, the color-signal components maymodulatey the subcarrier Wave signal at the transmitter in a differentphase sequence, for the purpose of minimizing the visual'eifects ofcross talk caused by deriving the color-signal components at thereceiver at improper phase angles. For example, the green, blue, and redcolor-signal components may modulate the subcarrier wave signal in thatorder during one eld of scan and in the order of green, red, and blueduring the successive eld of scan. In addition to the modulatedsubcarrier wave signal, a signal representative of the brightness of theimage is also developed at the transmitter and combined in aninterleaved manner with the modulated subcarrier wave signal to yform ina pass band common to both signals a resultant signal which istransmitted in a conventional manner.

A receiver in such a system intercepts the transmitted signal andinitially derives therefrom the modulated subcarrier wave signal and thebrightness signal. The modulation components of the subcarrier Wavesignal are then detected by a deriving means which is designed tooperate in synchronism and in proper phase relation with the subcarrierWave-signal modulating means at the trans- "ice g mitter. lAs describedin the previously mentioned application, Serial No. 207,154, thesesignals may be effectively derived from the subcarrier wave signal byderiving the quadrature modulation components thereof. It is desiredthat the deriving means `develop at its output circuit color-signalcomponentsv `which correspond in all their important characteristicswith the components utilized to modulate the subcarrier wave signal atthe transmitter. Furthermore, since several color signals modulate thesubcarrier wave signal at ydifferent phase points thereon, it isparticularly important that the deriving means at the receiver operatein proper phase relationship with respect to a predetermined phase ofthe modulating means at the transmitter. The color-signal componentsderived at the receiver are combined with the brightness signal toreproduce on the image-reproducing device of the receiver a color imagecorresponding to the image being televised at the transmitter.

In a receiver in accordance with the improved colortelevision systemdescribed in the copending application, Serial No. 207 ,154 previouslyreferred to herein, the phase sequence in which the color-signalcomponents are derived is changed periodically in synchronism with acorresponding changefat the transmiter. The color-signal componentseffectively are derived in the previously mentioned one phase sequenceduring one group of scanning fields, for example, in the sequence green,red, and blue. During another group of scanning ields interlaced withthe firstmentione-d group the color-signal components are derived inanother phase sequence, for example, in the sequence green, blue, andred. Therefore, in order that the color signal-deriving means in thereceiver be properly controlled to derive the color-signal components inthe proper phase sequence, it is ydesirable to develop a control eiectrepresentative of the change from one sequence to another and indicativeof the sequence which should be employed at any given time. Since thesesequence changes occur in relation to the fields being scanned, if thetields can be identified as odd-line or even-line elds, then a controleffect may `be developed to define such fields and the type linestherein. Such a control effect can then be utilized to assure that theproper phase sequence occurs during the identified field. In thismanner, if such synchronizing of the phase sequences at the transmitterand receiver occurs on identiied iields, then` --ferred to hereindescribes a iield-identication system` which effects the result justdiscussed. Though the sys#V tem described in the last-mentioned patentis generally suitable to etect field identification, it is not as immuneto` noise pulses which simulate line-frequency pulses as might -`f`A beIdesired for some applications. The present invention is ydirected to aheld-identification system which is substantially more immune to suchnoise pulses.

It is an object of the present invention, therefore, to

provide for a television system a new and improved field-V identicationsystem which is relatively simple in con-Q struction and stable inoperation.

It is another object of the present invention to provide a new andimproved field-identification system for an odd-line interlacedtelevision system for identifying ythe even-line fields with respect tothe odd-line iieldsf and which is relatively immune to noise pulses.'

It is still another object of the present invention to' provide a newand improved `field-identification system foruse vin an odd-lineinterlaced television system whichV I is capable of utilizingconventional television synchronize Patented July 2s, lassVY ing pulsesto electv the videntiiication of the different with the accompanyingkdrawings, andi its-scope will-be pointed out-in the; appendedclaims.

inthe drawings? jli-g. l l is aschematic diagram representingl acolortelevision receiver embodying'- a field-identification .system inaccordance with one form' of the invention;

Figs. 2, Sand Gare circuit diagrams including modiedj forms of portionsof the eldhidentication system of` Fig-- 11,Y .and

3 a, ElibV and `4` are graphsA utilized in explaining the operation ofoneormoreof the modiiicationsof Figs. 2,.,5Laad ,6.-

@cambiare-fiction ,01E receiver of. Fig- 1- Referring now tol-iig.- -llof the drawings, there -is-represented a colorftelevisionreceiver of thetype employed inuanodd-line interlaced-'televisionsystem and, particu-rlarly, ofthe type employed inthe improved-color-television systemdescribed inthe copendingapplication, Serial- No. 4207,154 previouslyreferred to herein. The receiver includes a radio-frequency amplifier Yof one. or more stages' having an input circuit-coupled to an antennasystem 11, '151; outputV circuit of the amplitier 19 inthe order namedare anoscillator-modulator12,- an intermediate-frequencyamplilier 13 ofone or more stages, a detector and auto` matic-gain-control` (AGC)supply 14, al video-frequencyamplilier 15 of oneor more stages, and a0-4- megacycle filter network 1,6. 'The outputV circuit of the network15j coupledI to an intensity controlelectrode of a cathoderay tube in animagereproducing device 1-7. 'Illia cathode-ray tube mayJfcr example,ccmprisc-y av single,V tube having a plurality ollcathodesAindividuallyresponsiveto thediierfent color signals, andan arrrangementfor directing the beams emitted from the separate cat lioles ontoAsuitable color-phosphors. SuchV a tube is moreiplly described in anarticle entitled "General Deseriptionfot Receivers forthe-Dot-Sequential Color Television System Whichv Employ Direct-ViewTri-Color Coupledf in cascade -Iwith theu207,154 previously referred toherein. Voltage dividers Y2G-and26b lare connected-across thel output-circuits dividers..2lia and- 26b andfapair of anodesiontly coupledLthrough .adoad resis t.0.r,2f5,-y to asource of potentiall-B and to theremaining one of the cathodes in thevcathoderay tube of the device 17. Acolor wave-signal generator 31,v which may 'be a` conventionalV.Sine-wave oscillator for developing a signal having -a frequency of,approximately 3.5 megacycles, is connected to an `input circuit in eachof the detectors ZI'rzJ-.andgZlbL The phase-delay circuits 19a and 19bare proportioned to delay the phase of the signals applied thereto byapproximately 90 and 180, respectively for a signal having a frequencythe Samaras. tiranni ahcfsignal-.fdcvclcp-cd-ic thc unit .31-

- nautilus rfcuitncffthc. unitlflacis coupled, thronghasynchronizing-,signal separator 28- to li-nefscanning and nem-spanning-windings- 33 in the .device 17 through a lincgtrcnucncy' generator,2.9- and4 .a held-frequencygen-6P atorlg irespectively.v TheseparatorZS isalso connected. to.;annimmt;,circuitt ofthe generator 31and to a pair-of.Y terminals 35,135: in .aecldrdenticaton system 32 fora- Plllpose .which be described more vfully hereinafter- The;gcueratorsll and' 3.0- arc.- -additicnally wlllllctdr Kincsccpcs in theRCA Rcvicw for June 1950, at paar-Sv 228 23,2, in,c lg1 s i ve It beunderstood-that other Suitable types; 0i color-televisionmcse-reproducing, de

vices .may bc cmplcycd- Y .Qccnlcd-in cascade with; anothcrcutputcircuit of. the

lt netwo r k 1 8, a phase-delay circuitv 19a, asynchronous deteetor 21g,a 0-1.5 n 1egacycle filter network 22a, and cnc 0f the cathcdes 0fkthccathcdcfray tube in the device v17. The output circuit ofthe. network18- is also coupled cithcrfthrcusllcphascfdclav circuit. 1912 andaSwitching, device 2ll..fc.r dr'cctlytllrcusllv thcV Sv-'itchine througha pair of terminals 36, 36 and a pair of termi. Halse-42,. 4.2arcsncctivelv, tothe unit .3.2.

An .additional output circuit cf, the unit 14, Specifically of the AGCsupply therein, is connected to the inputciremisor-lone or more-cf thetubes-cf :the radio-frequency mplier i0-, thccsc-illatQr-mcdulatcr'12,andthe inter. mediateffrequency amnliiier 13 ina well-known manner,-tolmaintain thesignalinput tolthei detectorlf-i witli;i.11.a-lrelatively nar-row rangefor 1a `wide ,range ot received signal.;intensities. com tected..` .to the output .circuit ot theintermediatefrequency amplifier 13 and may liaverstages` of interme.`diateffrequency amplification, a soundsignal d etQQtQr, stagesy ofaudio-frequencyv amplification, and a, sound.- reproducing device.

It lbei understood that the varionsunits thus fardescribedv with theexception-r of. the4 fieldridentitication,

system--321-may be 4of i any conventional rconstruction and;r

design'. The details-of .such units. are well. known in the.;

art andf1=aremore--f-ully described in the copendin-g -appli.

cation, Serial-No.- 207,154 previously referred toy herein, thereby-yrender-i-n-g a further description. thereof unnecesv sary-.

` G 'enerall'operation of receiverV of Fig; 1y

considering briefly the operationfoi the receiver .vorJ Fig. v las.Aa--whole, itwi'lll be assumed that;the,-;ield

ridentiiicationi` system 32 is al system Vfor; controllingztheoperation-ofthe switching, device I2lttoefiect either direct,

coupling of--the--outputfeircuit-fof the unit 18 kvto the/de` andsupplied to thetdetctQr 14vvherein its. modulation;

components. are derived. 'Ilhsc modulation componentsare-translatcd-through the. amplifier 1.5', and include alletl-mc'gacvclc.- brightncsscompcnent which is translated"thrcugllffthcdlcrnctwork 16, and. appliedto the intensity,control-,lclectrodesot thc. cathodefray tube in` the; device. 7.'.modulation A.comp@neufs derived in the aafla.o

soundsignal reproducing, unit 34, is alsocoupledvto l an output Acircuity of -the line-frequency generator 29.

The Apulse-responsive Ycircuit additionally includes a control system;jointly 'responsiveY to Vthedeveloped pulse signals and ftheldevelopedcoincidence `signal for developing a-control fsignal representative of-the ytime relation ofthe line-frequency pul-ses and theygroups ofiieldfrequency pulses. This-control system includes-:thesignal-combiningcircuit 39 `jointly 4responsive to the developed,pulse`signalsappliedto the terminals l36,1136, thesesignalsbeingf.representative -of line-frequency pulses, Vandtofthedeveloped-coincidence signal appliedfrom the unit 40 for combiningthese signals to ldevelop resultant signals.

4 A l control circuit -68 'is coupled between the outputcircuit-of-the-unitf39 and through terminals'37, l37 tothe switchingdevice Z0. rAlcircuitdiagl-am vof the unit 38 is represented in Fig. 2and this unit will now be described.

The lunil: l38 Id'S-ia keyed-detector Circuit E80 cmprising atriode481-having a control electrode coupled -to Yoriejof uthc terminals'43, '43, the other terminal 43 being-'effectively coupled to oneterminal of the cathode loan 'circuit ofthe fb'e 81. 4This cathode loadcircuit iiiiprises` a portion of a Avoltage 'divider having'seriesconnected :resistors '83, 84, 85, and '861 coupled -across -asource of B potential. The cathode of "the tube l81 is connected tothejuh'tion'of'the resistors v83 'and 84, the resistor 8'5aujnsfble,tlic"resistors'84 and '85 are 'bypassed A'fr 'signlen'ergyby'a condenser 87, and the resistor "86 is additionally a cathode-followerload resistorfor 'a tiiode 88 offa keying circuit 90. The anodeofilic-1tube88'is'difcct1y connected to a source of potential A-f-Bwhile the control electrode of-`this tube is cpled'to'a'psitivepotntialon a 'voltage -divider comprisingseries-c'onnected 'resistors 91 and 92coupled across 'a source ofB potential. Tire 'control electrode of thetube "88 is 'also icopled'through a condenser 93 to one ofthe 'terminals"42, 42, 'the other 'of these terminals being 'elect'ivelyconnected tothe cathode circuit of the tubel88.

The anode "o'i fhe detector'tube 81 is connected to a source 'ofpotential -l-B on a voltage divider comprising s'riesiconecte'd'resistors 464, 65, 66, and 67 vcoupled acrss a 'source l'of Bpotential, -and is also connected through a coupling condenser '68coupledl across the resistor-66'@ the control electrode of aitriode 69.The ciciiit'iilu'dingthe triode vacuum tube 69 and a similar tube 70comprisesV a vtrigger or counting circuit of the Ecles-'ordantype havingtwo stable operating conditions. The cathode's of'the tubes y69and'70'are jointly connected through a cathode load resistor V'.l to thelow potential terminal of 'a source of potential +B. The anode of thetube 'T0 is connected yto the junction of resistors 65 and 66forpotetial i-B and eiectively rthrough the condenser 68 to the controlelectrode of the tube 69. Similarly, theanode ofthe tube 69 isconnectedto a 'point of potential -lfB on-a voltage divider comprisingseries-connected resistorsZ, i7'3, '74, andv 7S` coupled acrossthe-source of potential =.1B,'this anode also being connected-through acondenser 'lcoupledl across- `the resistor 74 to the contro'l electrode'of the tube 70. The output terminals 37, 37 of the 4unit -38 areindividually connected to the anode load-fcircuit'of the tube' 70 at--the junction of resistors 4(ifi and 65Yfand-to theanode load circuitofthe tube 69 at the junction `oi? resistors 72 and 73. The controlelectrode of the `tube 'l0-is also coupled through a couplingfcondenser94 tothe cathode load fresistor'86 of the tube T88.

The Afield-identification `system 32 of Fig. l1 also'includes adisablingcircuia specilically a portion ofthe control circuit-38,yresponsive to the control 'signal developed jin the control rsystemIii'1clxding the unit 38 fandelective substantiallyftox diminish theresponsefofthefpuls'eLresponsive circuit and,fmoreparticularly, thecontrol system thereof toisignalsfrelfed?tothepreviously'mentionednoiscpulss. 'Ihe circitfelenrents fof'fthe disabling circuit Y-areIso-proportioned that the unresponsive period {thereof-has a durationsubstantially less than -the=interval betweensuccessive groups of thelield-frequenc :y pulses, 'More specifically, referringvto the circuitof AFig. Z, this disabling 'circuit comprises a time-constant 4networkincluding vthe dondenser v68 and 'at rleast theresistors Y66 and 67.-FAIhej parameter-sof thisnetwork are so proportionedjas to developa-tirne constant which has `a value substantially lessihan the intervalbetween successive v.groups of the-eldfre quency pulses but which isgreater than the durationof the conventional vertical retrace .pulseoccurring in--the circuit including the terminals 42, 42 during theretace interval-'ofthe iield-synchronizingsystern. The condenser 76,together with-theresistors 74 and 75 may -also beproportioned-to provideva similar, specifically Ya duplicate, time-constant `net-work in thecircuit 'including' the l tube 70. -The condenser -94 in cooperationwith the-resistive components in -the input circuit' of the Ytubej 70comprises a differentiating circuit Eetfective to dilerentiatethecpulsesignal developedacross the cathode=loadresistor 86. The control circuitsoft-he tubes 69 and 70 Aare so biased that these tubes are effectivelytriggered Yonly `by negative going pulses.

Explanzian f ope'tnimi offild-demjdton .S'ys't'eiiz v'32 of Fig. '1

In considering the operation of the field-identification system`3i2vo`fFig. -l reference is made tocurves '1i-G, inclusive, of Figs. 3a andA3h, each curve having coordinates of time and amplitude andrepresenting vthe wave forni of a signal effectively associated with aspecific circuit in the system 32 of Fig. 1. The compositevsynchronizing signal, including the line-frequency ,and-held? frequencypulses-as represented by -curve A of Fig. 3a for one eld of scan andcurve A of Fig. 3b for an interleaved lield, and noise .pulsesasrepresented by curve A in'Fig. 3b, is applied vto the terminals 35, y35from aunit such a's the signal separator 28 of Fig. 1. As described morefully in the United States Patent No. 2,6'97,`744, the {Yield-pulseselector 41 is effective to select the field-fre` quency pulses of thesignals lrepresented by curve vA of Fig. 3a Vand curve A of Fig.3b.These selected pulses are applied to the resonantcircuit '40tofshock-excite -by means of both the leading and trailing edges ofthesepulses the resonant circuit 40 suflciently to develop an outputsignal therein having in the absence of a noise -pulse such asrepresented by curve A' of Fig. 3'b the waveform represented inidealized -form by curve AB of Fig. 3a, this signal being applied to thesignal-combining circuit v3'9 in the control system including the units-3`9 and 3'8.A When a noise pulse such as represented `by curve A ofFig. 3b overrides the trailingv edge of a-group of `fieldpulses therebycausing the field pulses -to be apparently terminated at a later timethan normal, an output signal having the Wave form represented by curveB of Fig. 3b is developed in Athe resonant circuit 40. It is apparentthat the portion of the signal occurring during the interval t3-t3 andrepresented b`y a portion of curve BV of Fig. 3'b doesnot yhave the sametime-space characteristicin its iield of scan vas th'e signalArepre'sented by curve B of Fig. 3a does Vii1its iiel'd of scan andlthat the 'dilere'nce is caused 'by the noise pulse representedby'c'u'rve A of Fig. S'b.

There is also applied'to the controlv system, specically, to the unit 38through terminals 42, 42 a pulse representative Ao'f the conventionalfield-retrace pulse represented by curve C iii-both Figs. sa and 3b and'normally developed in' the system 'including the vfield-Virexfie1`1`cygenerator 3i) and the yfield-deflection portionof vthe wiiid ings 33during the retrace period of each field of scan. rn audition, pulsesignals, specifically, line-frequency pulses' occurring during'horizontal retrace, and havingth'e waveform represented by lcurve Dj ofFig. 3a are applied to thc-'control system-and, specifically, todesigual-'conininiog circuit "39 therein through the terminals '36; "36during one 'field fof scan. 'During another neldors'can 9 analogouspulse signals having the wave form represented by curve E of Fig. 3b aresimilarly applied to the control system.

As described in United States Patent No. 2,697,744, the signals havingthe wave forms represented by curves B, C, and D of Fig. 3a effectivelycombine to develop composite signals as represented by curve F of Fig.3a at the input circuit of the control circuit 38, specifically, atterminals 43, 43. As explained in the patent just mentioned, the waveform reprented by curve F is effective to identify one field withrespect to an adjacent field by a determination of the time relationshipof a line-frequency -pulse with respect to a peak amplitude of thesignal represented by curve B of Fig. 3a. Effectively the timing of thefield-frequency pulses is compared with that of the line-frequencypulses to determine the character of the field. As explained in thelast-mentioned patent, in accordance with present television standards,the line-frequency pulses have such a time relation with respect to thefield-frequency pulses during one field of each frame as to coincidewith peak amplitudes of the signal represented by curve B of Fig. 3a andthus to cause the signal represented by curve F to be developed. Duringthe other field of 'the frame the line-frequency pulses represented bycurve E of Fig. 3b should occur in such time relation with respect to asignal of the type represented by curve B of Fig. 3a as to develop acomposite signal analogous to that represented by curve F but in whichthe line-frequency pulses represented by curve E do not coincide withpeak amplitudes of the signal represented by curve B of Fig. 3a. Thisdesired result may not be obtained a noise pulse such as represented bycurve A of Fig. 3b occurs. In a manner now to be explained, such a noisepulse may cause line-frequency pulses to coincide with peak amplitudesof the signal developed in the resonant circuit 40 during both fields ofa frame. This result prevents identilication of one field of the framewith respect to the other and causes any apparatus such as the switchingdevice of Fig. 1 which is controlled by signals representative of suchidentification to operate incorrectly.

As previously explained herein, during the other field of the frame theresonant circuit 40 will initially be shock-excited at the proper timet1 to develop a signal such as represented by the portion of curve B ofFig. 3b in the interval tl-tz. Since the trailing edge of this group offield pulses is encumbered by a noise pulse such as represented by curveA', the circuit 40 will be shockexcited by the trailing edge of thenoise pulse at a time t2 later than normal to develop a signal duringthe interval t2-t3 out of phase with the initially developed signal andrepresented by the latter portion of curve B of Fig. 3b. The compositesignal represented by curve,

B of Fig. 3by is combined in the signal-detection circuit 80 with thesignals represented by curves C and E of Fig. 3b effectively to developa signal such as represented' by curve G in the controlelectrode-cathode circuit of` the unit 80. It is apparent that theline-frequency pulses represented by curve E properly occur at thereference Yaxis and -not at the peak amplitudes of the sine wavedeveloped in the unit 40 during the portion of the signalrepresented bycurve G occurring during the interval. t1-t2. However, during the'interval t2-t3, due to the.

shift in phase of the signal developed by the resonant circuit 40, atleast some of these pulses occur at the peak amplitudes of the latterportion of the signal represented by curve B of Fig. 3b. As a result thefield-recognition system is ineffective to discern any difference in thetwo fields of the frame and develops similar control effects for eachfield. It is a principal purpose of the present invention to provide adisabling circuit which will prevent such erroneous response.

Consider now the circuit of Fig. 2 and the curves l-N,

inclusive, of Fig. 4, each of the latter Acurves representmgthewaveforni of a signal aissotatedk with a speciic point in the `circuit ofFig. 2. The reference characters Bl-B-I, inclusive, indicating potentiallevels with respect to these curves and with respect to curves O and Pto be considered hereinafter refer to the positive potentials of thespecific circuits at an arbitrary time t0. Similar reference charactersare utilized in Figs. 2, 4, and 5 to indicate the points in the specificcircuits having these potential levels. The field-retrace pulsepreviously represented by curve C in both Figs. 3a and 3b on an expandedtime scale is represented in idealized form for seven fields of scan bycurve l of Fig. 4 on a reduced time scale. This retrace pulse is appliedto terminals 42, 42 of Fig. 2 and is effective to develop across thecathode load resistor 86 a corresponding pulse which is differentiatedin the circuit including the condenser 94 and the resistive componentsin the input circuit of the tube 7i) to have a wave form represented bycurve K. As previously explained the tubes 69 and 70 are responsive onlyto negative-going pulses and, therefore, the negative-going portion ofthe differentiated pulse represented by curve K is effective to controlthe operation of the tube 70` in a manner to be described more fullyhereinafter. Signals such as are represented by curves F of Fig. 3a andG of Fig. 3b are applied through the terminals 43, 43 of Fig. 2 to thedetector including the tube 81 and are effective :to develop resultantsignals in the output circuit of the tube 8l for application to thecontrol electrode of Ithe tube 69. The output signals developedvfrom thedesired signals as represented by curve F of Fig. 3a are represented bycurve L of Fig. 4 While an output signal developed from the undesiredsignal represented by curve G of Fig. 3b is represented by curve L1 ofFig. 4. The desired negative-going pulse signals represented by curve Lare indicative of fields of similar types, that is, either odd-line oreven-line fields Whereas the undesired pulse represented by curve L1 isa spurious response which indicates the occurrence of a field of onecharacter when actually a field of another character is present, and iseffective to disturby the operation of the field-recognition system.

Considering now, more specifically, the operation of the trigger circuit60, it will be assumed initially that the tube 69 is conducting and thetube 70 is cut olf at time to and a signal such as represented by curveM of Fig. 4 is being deevloped in the anode circuit of the tube 70. Attime t1 a negative-going pulse as represented by curve K, being aportion of the derivative pulse of the vertical iiyback pulserepresented by curve I, is applied to the control electrode of the tube70. Since the tube 70 is at cutoff, this pulse is ineffective to controlthe operation of the trigger circuit l6l). At time t2 a negative-goingpulse as represented by curve L, being representative of the type offield being scanned, is applied through the condenser 68 to the controlelectrode of the tube 69. The latter pulse is effective to cause thetube 69 to become nonconductive and the tube 70 to become conductivebecause of the signal applied to the control electrode thereof throughthe condenser '7 6 from the anode of the tube 69. This status ofoperation is maintained for approximately one field of scan until a timet4 when a negative-going pulse as represented by curve K is applied tothe control electrode-of the tube 70 through the terminal 62 to causethis tube to become nonconductive and the tube 69 to become conductive.This type of operation continues at substantially a field rate until thetime t8. At the time ts the negative-going pulse represented by curve Kis properly effective to render the tube 70 nonconductive at a time whenit should become nonconductive. As a result, the spurious pulse L1, atthe time t9 when applied to the control electrode of the tube 69 fromthe output circuit of the detector 80, is effective to cause the tube 69to become nonconductive and the tube 70 to become conduc-4 tive at atime when such operation of these tubes should` not occur. Thus, anerroneous output signal is develf oped in the output circuit includingthe terminals 37, 317E gsoegeoo to'c'outrl the Aoperationf theswitching'device 20fin1fig. 1 "during "the period 2921415. At'fthe 'time"t 'tlieiiegativegoing pulse represented by curve 'K- is 'effective tocause the :tube 70 to ybecome Xiionconductiyeand the tube-59 -to becomeconductive land at tlie'time tm 'the'ieve'rse-action prperly'occurs-dl'ie tothe ajgrplication Vot a negativeegoing pulse represented bycurve L to'V the control electrode of the' tube 69. Thereafter, no:otherfsnurios pulses being applied to the cbntrolelectrbdefof the fbeY69, the system 'operates properly.

-Itis apparent that if'the triggercircuitilopera'tes lin a manner todevelop -a `signal Aas yrepresented by 1curve M during the period tgtlg,theswithingdevicev'z() ofFig. i would causeY the`syiichronous detectorsy22111 -ahd '216 to-derive thev color-signalcoiiipnents in improperphasefsequence and,v thus, `cause improper colors to bedeveioped in theimage-reproducing device 17 'of vFig. l during'this interval. y'Sincethis effect occrssubstantially throughout the' duration of 'one field`it would be lapparent to a iiiewer and is therefore highly/'undesirableTo fprevent suchV an effect fthe disabiing'circuit previously-described-heeiii `is coupled to the trigger circuit 60 inthe control Ysystenr'oiFig. 2 todeseils'iti'fze l'th'e"control 'system With respect to schnoise pulses.

As previouslydescribedherein, the network including the condenser 68'and atleast Vthe'resistors'"ft'iand 67 iS proportioned to have'fa' finieconstant substantially longer than the duration of the vertical retraceAj m'll'sie 'represented lby curve '1. 'Additiorallthefnetwrk includingthecondenser 76'ar'id at l'eas't resistors 74 and 75-is4smilarI-yproportioned. Keferi'ingfifow to curve-Naf Fig. 4, as'thesignal derived Lfroin the Vertical `retrace pulse 4and represented by'curve 'K-'is'eictve torender' the tube 70 nononnuniive andthe 'tube@conductive nt the time f, thev time constant of the network includingthe condenser 6s is effective to' develop positive potential on the 'comel'lerectro'de vof tube' v69 of 'a magnitude represented by theamplitude ofcurve N at tiinet. i '-Ihisp'o'sitiyep'- tenda-1 graduallydecay-'sito' becoxne a flinchy lower positive potential B at time tu,the period 'tar-"tf1 beingsubstahdaily llonger' than theldrtion'lrBL-fmof 'ine ye" ial reti'ee pl'se. Tli1is,"wlien tiies'uiouspl's'ererp f lay-survol, occurs -ar't-inre'rg, it 'is ineffectiveff dfeine donll elect'ode f the E'tubie`-^'69 to' s'iclil Aiw'triitiallfas tornder" the' tlibe`69'nicoiil1ct-iv'e'.

As a-re`s`l't'the" G'irC'uit '60 is' I"eiiil'fet-l lii'nspsii/'e 'fo'plssfers' lVe f noise applied 'to the trigger circuit f'rofn "the'detector 80 for an interval substantially less the jii1't`ei'iil'be'-`tWeen L4'the 'successive Sgrdups of the iild-fr'eqleioy pulses rldisubstantially longer` thantie durtibn'fithe Vertical retraceffpu'lse.Since thevert'ical'retr-ac'e pulseerpes nted lay-curve K also "act's'asakeyihg-pulse'to render tectorincluding theiube $1 ndut'iie onlydiiriiig the period of this-pulse, theA trigger circuit 60'neednotbelndered unresponsive for a 'period -muc'h'lbnger tlianfth'atof the vertical" retrace pulse. Though tliep'resentinifnton isdircctlyconcerned only With 'the' r sponse fthe'tub'e `69 to' lpulses appliedthereto, Zthe response Loff'lthetulie 7i) :is controlled in a mannerIs`inil`ali`to that tlie vtube s'in# dicted `by the exponential "typesig'ii'al vvthe niegztiiie going portionof curveN. More specifically,j-iistlas'the exponential portion of the 'signal initiated at A'-tiine"tg uis effetiveto biastliecontl'ciciitif'tlie'tube 569sb'higlilypositivefas to renderthe tbe"69 unresponsive' -to negative pulses ofnormal amplitude, the exponential port-ion tiatedat time 'tig iseffective inl'an 'opposite vsense 5to' cause the control circuit of thetube 70t`o be biased t-sch a high negative potential-'as torender the'tube 7i? uspnsive, during the Iperiod 'titfg to the-positive ''f normalamplitude which Would Ibeppliedto 4tiie'tlilfie 70 fromthe anode of thetube 697if the tube69beanicnconductive duringthis'period. flBysuchidulcoi'tol the tov erroneous -triggcriiztg' yis increased.

' e'applicantdoes notintend "to limit-the invention edeft2, nais sanina. '74

Resistors@ n 330 kiohns. usisrorsir 'and 7s i801 kilnms. Resisfdrfgfi'sc kildhnis.

uesisfrjss so'kilonnis. Resistor s 4 V,27o kilohins. Resistor `250liilo`h'1`s.

Resistor so 3.3 ki'lohni's. uesisfrgisgs nigoh'ns. uesis'fwz 1,5jineghms l Cnaensesjfjqs and 76 'assoc` nierm offas". condenser?? on@retornan cndenserjss n.047 fniroffd. Condenser '94 200naerpinier'ofras; Tte "69' I1/2 type 12.4.17. Tube 10 type 12u17. inne-Vs1 1/2' type nary. Tubsss l/zjiypej'izAw. +B 25o vous. Amp' une 'ornurses ppiied fo v s,

'fefnnals' 42, 42 soyons. Amplitude organises' apired to l terminals 4s,'es l'35 'vous Dscription md explanation of op'rafionlofporzionofeld-:l'dhl'''r .syfm' 'epshtd i by Fig. -5 There has beefndescribedherein with reference vto Figs. 1 rand 2 a hid-identification systemwhich `isfrelatively immune t undesiredjnoise pulses and in which thedisabling circuit 4toveffe'ct such immunity is a time-constant networkinthe input circuit of the trigger circuit. It may -be desirable forsomeapplicationsto liect such disabli'ngv at avr-point inthe*iieldidentiiication'system prior to the input circuit of the triggercircuit. Y The arrangenient of Fig. Smaywbe employed for the latterpurpose. Since the circuit-of Fig. 5 is siriilar` to the-circuit'of Fig.2, similar are designated by lthe same reference nurrieralsand analogousunits are designated inw-the circuit ovf'FigfS by the same referencenumerals ivitha prefix f S. l the circuit arrangement represented byFig. 5 the triggr'circuit 6i) and the detector circuit 80 are repre-4sented inb'loclgform since these units are theusarne asthe units 60'ndf'i), inthe arrangement of jkFig. The arrangement of Pig. .5 diifersifrorn* that of Fig. 2 in that a feedback circuit including 'atime-constant network having va series-connected condenserm97 and aresistor 96 is coupled 'through the terminal :63 to the contrqlelectrode'circ'itpfthe tube '69'in the trigger circuit di). ',I'he finie constantof this 'network'is substantiallylbnger than 'the duration oi Vthe`vertical retrace pulse'hrepre.- s nt'ed by c'irmifejl. The junction ofthe resistor -96 and the vcondenser 97`isfciipled'to a control electrodeof a iode`l9lv5, thelaodfe of 'yi/lich is connected to a source fpotential and 'the 'cathode of which Ais connected tothe 'carbone' 10aa'resistor "sa o Theopertoli of,A 'fe i'rcuit arrangement of Fig. is' t6'that fof fthe arrangement of Fig. 2 vexcept for 'the di'sabliiigciiclitincluding the 4time-constant net- Wo'rlc '96, SIT'and` theibegs. Theoperation of this disabling' fc'i'r'cuit'` Will 'nyifbe described with'reference to crye's I, Llfd Odf Fig. '21. The lsaine conditions foperation 'iiyill'be a'sshid as pr'eifiously assinediiith respect'topnefreun laff-sag'ennin of Fig. 2, 'that' is, 'that theltb'e 69" isc'foidli'ctiiigy 'tl'1"e tube 70`is Yat'cit 'ff at to. At 'e 'il "thm"pulse occurring 'during the vertical renace -poreio'n of uiejrpr'oduaifn'ge anu ppd, i.

control electrode of the tube 95 to be suiciently positive to permitcurrent to flow therein. Consequently, a small positive potential isdeveloped across the resistor 86 by the current ow in the tube 95 atthis time causing the step portion in the interval :f1- t2 in thenegative-going pulse of the signal represented by curve O. At time t2 asdescribed previously herein, the tube 69 in the trigger circuit 60becomes nonconductive while the tube 70 therein becomes conductive. Atthis time very little if any current iiows through the tube 95 and thefull elect of the pulse represented by curve I is developed across theresistor 86. At time t4 a pulse representative of the vertical flybackpulse represented by curve I would normally be developed across theresistor 86. At the same time the tube 70 in the trigger circuit 60becornes nonconductive and a positive pulse of large magnitude isapplied to the control electrode of the tube 69 torender this tubeconductive. This positive pulse of large magnitude also develops apositive signal across the vresistor 96 causing a large current to flowin the tube 95. The current flow in the tube 95 develops a largepositive potential across the resistor 86 which counterbalances thenegative pulse which would normally be developed thereacross. Thus, asaw-tooth type signal as represented by the portion of the signalrepresented by curve O between the times t4 and t7 is developed acrossthe resistor 86 preventing the detector circuit 80 from operating atthis time. A similar disabling action occurs between the times t8t11.Therefore, the noise pulse represented by curve L1 is ineifective at thetime t9 to trigger the trigger circuit 60.

Description and explanation of operation of circuit arrangement of Fig.6

There has been described herein with reference to Fig. 5 one circuitarrangement for disabling the held-identication system at a pointtherein prior to the input circuit of the trigger circuit 60. Thearrangement described with reference to Fig. 5 utilized a disablingcircuit including an additional time-constant network and anelectrontube in order to apply a disabling signal to the cathodecircuitof the detector circuit 80. It may be desirable to eiect a similarresult without utilizing such additional elements as the components 95,96, and 97 of Fig. 5; YThe circuit arrangement of Fig. 6 may be employedto effect such a result. Since thearrangement of Fig. 6 is similar tothe arrangement of Fig. 2, similar elements thereof are designated bythe same reference numerals and analogous elements by the same referencenumerals with a prefix of 6.

The arrangement of Fig. 6 differs from that of Fig. 2 in theproportioning of the resistors 683, 684, and 685 and of the condenser687. In addition, the resistor 683 instead of being coupled to a sourceof potential +B is coupled through the terminal 61 to the anode circuitof the tube 69 in the trigger circuit 60. The resistors 683-685,inclusive, and the condenser 687 are proportioned to provide a timeconstant approximately equal to the interval between successive fieldpulses.

Considering now the operation of the arrangement of Fig. 6, it will beassumed as was assumed with respect to Figs. 2 and 5 that in the triggercircuit 60 the tube 69 is conductive and the tube 70 is nonconductive atthe time to. Referring now to curve P of Fig. 4, at the time t1, a pulserepresentative of the eld retrace pulse is developed across the resistor86 and is effective to render the -tube 81 conductive during theduration of this pulse. At the time t2 the tube 69 in the circuit 60, aspreviously described herein, becomes nonconductive while the tubev 70 isrendered conductive. As the tube 69 becomes nonconductive the anodepotential thereof rises and is applied through the resistor 683 to thetime-constant network including the resistors 684 and 685 and thecondenser 687. Thus, between the times t2 and t3 there is a slight risein the positive potential across this timeconstant network asrepresented by curve P of Fig. 4. At the time t3 the pulserepresentative of the vertical retrace pulse terminates and the positivepotential developed across the network including the resistors 684 and685 and the condenser 687 continues to rise to a relatively highpositive potential at the time t4. At this time the pulse representativeof the vertical retrace pulse is again developed across the resistor 86and the tube 69 becomes conductive causing the anode potential thereofto fall. Thus, due to the time-'constant action of the network includingthe resistors 684 and 685 and the condenser 687 and due to the presenceof the negative-going pulse across the resistor 86, an effect such as isrepresented at times t4, t6, and t, is developed. The negative-goingpulse occurring from time t4 to time t8 is not of suiicient potential tocondition the tube 81 to be conductive during this period because of thepositive potential previously developed across the time-constant networkincluding the resistors 684, 685 and the condenser 687 during theinterval t2-t4. The potential previously developed across thetime-constant network decays in the interval t4-tm An action similar tothat which occurs in the interval t4--tq also occurs in the intervalt8-t11. Since the charging of the circuit including the resistors 684and 685 and the condenser 687 is effective to nullify the normal gatingeiect of the negative-going pulse developed across the resistor 86during the interval tg--tm and the tube 81 is rendered nonconductiveduring this period, the noise pulse represented by curve L1 occurring attime t9 is ineffective to cause an output pulse to be developed in theoutput circuit of the tube 81 and consequently ineffective to triggerthe trigger circuit 60. It is apparent that the latter disablingoperation is eiected solely by properly proportioning the resistors 683,684, and 685 and the condenser 687 which are normally in the detectorcircuit including the tube 81. In addition to such proportioning, theresistor 683 is coupled to the anode circuit of the tube 69 in thetrigger circuit 60. Thus, the desired disabling eiect is accomplishedwithout utilizing additional circuit elements.

Though the held-recognition system in accordance with the presentinvention has been described herein as including various types ofdisabling circuits in order to effect noise immunity in the recognitionsystem, it is apparent that, generally, such noise immunity is obtainedby causing the field-recognition system to be operativeonly during ashort interval in each eld of scan, this.

interval being in the vicinity of the field-frequency pulses, and the`field-recognition system is disabled for a short period after it hasresponded during one of these intervals. Thus, effectively thefield-recognition system is operative only during a short intervaloccurring once in each frame. It will be readily apparent to thoseskilled in the art that many types of feedback systems may be utilizedto eiect this result in accordance with the teaching of the presentinvention.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modiiications may be madetherein without departing from the invention, and it is, therefore,aimed to cover all such changes and modicattions as fall within the truespirit and scope of the invenion.

What is claimed is:

1. In an odd-line interlaced television system a eldidentilicationsystem comprising: a circuit for supplying line-frequency pulses andgroups of field-frequency pulses and subject to supply Aspurious noisepulses, said groups of field-frequency pulses having one time relationwith respect to said line-frequency pulses during one group ofA fieldsand another time relation during interlaced fields;

signal-generating means coupled to said supply circuit and responsive tosaid held-frequency pulses for develop

